The fifth component of complement, C5, is the precursor for the important phlogistic molecule, C5a, a potent chemotatic agent. Sera from C5-deficient individuals lack bactericidal activity and have severely impaired ability to induce chemotaxis. Deficiency of C5 in the mouse has been recognized since the early 1960s and this model has been used to demonstrate the importance of C5 in the initiation of pulmonary inflammation. Improved methods for the analysis of protein synthesis by cells in culture and the isolation and characterization of cDNA for mouse C5 have allowed evaluation of the molecular basis of this protein deficiency. We have described both quantitative and qualitative differences between C5-sufficient (C5S) and C5-deficient (C5D) mice in the protein synthesized, in the C5 mRNA in cytoplasm and nuclei, and in the organization of the C5 gene. The experiments outlined in this proposal will extend these early studies to examine the defects in the C5 deficiency. We will define the structural abnormalities in the protein synthesized by the C5D cells that interfere with the secretion of the protein. cDNA libraries will be prepared from C5S and C5D mRNA and the C5 specific cDNA will be isolated and characterized to analyze the mRNA sequence abnormality(ies) responsible for production of the abnormal C5 protein. In addition, cosmid libraries will be prepared from C5S and C5D DNA and C5 specific clones will be isolated and characterized to analyze the structural abnormalities in the C5D gene responsible for the abnormalities in the C5D mRNA. Finally, C5S and C5D genomic clones will be transfected into mouse L-cells and the expression of the genes in these cells will be studied to examine the potential role of the C5D cells in producing the abnormalities in protein secretion. The transfected cells may be useful as a reagent for subsequent studies on the role of RNA processing in producing the C5 deficiency state.